Police have carried out raids on two houses linked to the man arrested in relation to the discovery of 39 bodies in a lorry in Essex.
The driver, named Mo Robinson, 25, from Northern Ireland, was arrested on "suspicion of murder" on Wednesday.
So far, investigations have revealed that the trailer containing the victims arrived at Purfleet from Zeebrugge in Belgium at around 12:30 am (local time).
Prime Minister Boris Johnson said the perpetrators of the crime "should be hunted down", with the police adding that the tracking route used "will be a key line of inquiry".

Russian drones injure 19, cause extensive damage in Ukraine's Zaporizhzhia
Israel launches new military operation in northern West Bank
At least 14 dead after fire engulfs residential towers in Hong Kong
Australian teenagers ask High Court to block social media ban
India lodges strong protest with China over detention of Indian woman
